Suspension structure

ABSTRACT

A suspension structure includes a subframe and a suspension arm. The suspension structure has strength lower than that of the subframe. When an excessive external force acts from a road surface on a wheel, the suspension arm is deformed before the subframe is, thereby preventing the excessive external force from directly acting on the subframe.

FIELD OF THE INVENTION

[0001] The present invention relates to an improved suspension structurefor preventing an excessive external force from acting on die-castsubframes.

BACKGROUND OF THE INVENTION

[0002] A known structure in which a subframe is mounted to the bottom ofa floor panel serving as a component of a vehicle body, and a suspensionarm is mounted to the subframe, is disclosed, for example, in JapanesePatent Laid-Open Publication No. HEI-9-66718, “Mounting Structure forAutomobile Suspension Member,” or in Japanese Patent Laid-OpenPublication No. HEI-6-340274, “Vehicle Suspension Cross Member.”

[0003] HEI-9-66718 describes a structure comprising a second memberhaving a hole and being mounted to a vehicle body, and a first memberhaving a protruding portion and being mounted to a suspension memberserving as a subframe, the first and second members being fixed to eachother via a fastener with the protruding portion inserted into the hole,thereby mounting the suspension arm to the suspension member.

[0004] When an excessive external force acts on the suspension armthrough a wheel of the vehicle, for example, force is transmitted to thesuspension member, breaking the fastener, causing the protruding portionof the first member to slip out of the hole of the second member, andthereby detaching the suspension member from the vehicle body.

[0005] HEI-6-340274 describes an integrally-molded aluminum alloysuspension cross member serving as a subframe, which has a body, awing-shaped portion and a plurality of vehicle body mounting members oneach side of the body, and an arm supporting member for supporting asuspension arm at the end of each wing-shaped portion.

[0006] In HEI-9-66718, it is conceived that an excessive external forceacting on the suspension member would cause the suspension member to bedetached from the vehicle body, thereby adversely affecting the steeringof the automobile.

[0007] In HEI-6-340274, even if the suspension cross member has astrength enough for normal operation, it is presumed that an excessiveexternal force applied from the suspension arm to the suspension crossmember cannot be sustained by the suspension cross member with such astrength and the suspension arm, adversely affecting the steering of thevehicle as was the case with HEI-9-66718.

SUMMARY OF THE INVENTION

[0008] It is therefore an object of the present invention to provide asuspension structure designed to prevent an excessive external forcefrom acting on a die-cast subframe.

[0009] According to an aspect of the present invention, there isprovided a suspension structure which comprises a subframe designed tobe mounted to a floor panel, and a suspension arm mounted to thesubframe vertically movably, wherein the subframe is die-cast ofaluminum alloy, and the suspension arm has strength lower than that ofthe subframe.

[0010] When an excessive force acts from the road surface on the wheel,for example, the suspension arm is deformed before the aluminum alloydie-cast subframe is. Thus the suspension arm mitigates the excessiveforce, preventing the aluminum alloy die-cast subframe from beingaffected by the excessive force.

[0011] The suspension arm preferably comprises a toe control arm andother components; and the toe control arm preferably has a strengthlower than those of the other components, so that the suspension arm hasa strength lower than that of the subframe. With respect to theexcessive force applied from the wheel to the components of thesuspension arm, the toe control arm is deformed before the othercomponents are, protecting the other components.

[0012] The toe control arm is preferably of a forged material. When anexternal force acts on the suspension arm through the wheel, the toecontrol arm is deformed but not broken.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Certain preferred embodiments of the present invention will bedescribed below, by way of example only, with reference to theaccompanying drawings, in which:

[0014]FIG. 1 is a perspective view showing a die-cast subframe and asuspension structure according to the present invention;

[0015]FIG. 2 is a plan view showing the die-cast subframe and thesuspension structure shown in FIG. 1;

[0016]FIG. 3 is a plan view illustrating the function of a suspensionarm when an external force acts on a wheel; and

[0017]FIG. 4 is a perspective view showing a toe control arm.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The following description is merely exemplary in nature and is inno way intended to limit the invention, its application or uses.

[0019]FIG. 1 shows a structure in which a subframe 10 extending in atransverse direction of a vehicle is attached to a floor panel servingas a component of a vehicle body, a suspension arm 11 is mounted to thesubframe 10 in a vertically movable manner, and a knuckle 12 serving asan axle supporting member is attached to the suspension arm 11. An axleshaft is mounted to the knuckle 12. A wheel is rotatably mounted to theaxle shaft via a hub.

[0020]FIG. 1 shows only part of the structure of the subframe 10,suspension arm 11 and knuckle 12 from one lateral side. The subframe 10,suspension arm 11 and knuckle 12 have a symmetrical structure.

[0021] The subframe 10 is die-cast from aluminum alloy and is a membershaped like a ladder in a plan view, having vehicle body mounting parts14, 15 for mounting to the floor panel, and upper mounting parts 16, 17and lower mounting parts 18, 21, 22 for mounting the suspension arm 11.

[0022] The suspension arm 11 has an upper arm 24 attached to the uppermounting parts 16, 17 of the subframe 10 in a vertically rotatablemanner, a first lower arm 25 and a second lower arm 26 attached to thelower mounting parts 18, 21, respectively, in a vertically rotatablemanner, and a toe control arm 27 attached to the lower mounting part 22in a vertically rotatable manner. The suspension arm 11 has such amechanism for hanging a rear wheel, for example, and constitutes a rearsuspension 28 with the knuckle 12.

[0023] The upper arm 24 has a first arm 31, a second arm 32, and a thirdarm 33. The first and second arms 31, 32 are attached to the uppermounting parts 16, 17, respectively. The third arm 33 is attached to afirst mounting part 35 of the knuckle 12.

[0024] The first lower arm 25 is attached at one end to the lowermounting part 18 and at the other end to a second mounting part 36 ofthe knuckle 12.

[0025] The second lower arm 26 is attached at one end to the lowermounting part 21 and at the other end to a third mounting part 37 of theknuckle 12.

[0026] The toe control arm 27 is attached at one end to the lowermounting part 22 and at the other end to a fourth mounting part 38provided at the side of the knuckle 12. The toe control arm 27 hasseparate arm halves 41, 42, an adjusting bolt 43 connecting the armhalves 41, 42 to each other, and locking nuts 44, 44 fixing theadjusting bolt 43 and the arm halves 41, 42, to allow fine adjustment ofthe toe angle of the wheel and maintain the finely adjusted toe angle.

[0027] The toe control arm 27 is, for example, of a forged aluminumalloy material and has a small sectional area so as to have a lowerstrength than the other components of the suspension arm 11, i.e., theupper arm 24 and first and second lower arms 25, 26, and than thesubframe 10.

[0028]FIG. 2 is a plan view showing the die-cast subframe and thesuspension structure according to the present invention.

[0029] A wheel 45 is positioned using the upper arm 24 and the first andsecond lower arms 25, 26 of the suspension arm 11. The toe control arm27 is used to finely adjust the toe angle of the wheel.

[0030] When finely adjusting the toe angle, the locking nuts 44, 44 arefirst loosened, and the adjusting bolt 43 is rotated to change the totallength of the toe control arm 27, thereby obtaining the desired toeangle. Thereafter, the locking nuts 44, 44 are fastened with theadjusting bolt 43 held and prevented from rotating. If the total lengthof the toe control arm 27 is set lower, a front portion 45 a of thewheel 45 inclines inward toward the vehicle, i.e., to the θin side, andthe wheel 45 has toe-in. In contrast, if the total length of the toecontrol arm 27 is set higher, the front portion 45 a of the wheel 45inclines toward the outside of the vehicle, i.e., to the θout side, andthe wheel 45 has toe-out.

[0031] The toe angle of the wheel 45 effects the steering properties ofthe vehicle during cornering, for example. Proper adjustment of the toeangle provides mild understeering with which the driver can easilycorrect the advancing direction (the vehicle tends to deviate outside ofthe path of circular motion).

[0032] Now the function of the suspension arm 11 as described above isdescribed with reference to FIGS. 3 and 4.

[0033] In FIG. 3, an excessive external force F as shown by an arrowacts on a forward portion of the outer side of the wheel 45, forexample, and the external force F is transmitted from the wheel 45through the knuckle 12 to the suspension arm 11.

[0034] In FIG. 4, the excessive external force transmitted to thesuspension arm 11 compresses and deforms the toe control arm 27 with thelowest strength among the components of the suspension arm. Since thetoe control arm 27 is of a forged material of high toughness, it is notmore severely damaged or broken.

[0035] The deformation of the toe control arm 27 changes the toe angleof the wheel. This, however, only changes the feel of the steering, thatis, provides less mild understeering or neutral steering (with which thevehicle tends to trace the path of circular motion).

[0036] As illustrated in FIGS. 1 and 3, in the structure of the rearsuspension 28, for example, where the subframe 10 is mounted to a floorpanel, the knuckle 12 is attached to the subframe 10 via the suspensionarm 11 in a vertically movable manner, and the wheel 45 is rotatablyattached to the knuckle 12 via an axle shaft, the subframe 10 isdie-cast of aluminum alloy and the suspension arm 11 has a lowerstrength than the aluminum alloy die-cast subframe 10. When an excessiveforce F acts from the road surface on the wheel 45, for example, thesuspension arm 11 is deformed before the aluminum alloy die-castsubframe 10 is, mitigating the excessive force F, thereby preventing thealuminum alloy die-cast subframe 10 from being affected by the excessiveforce.

[0037] Further, in the present invention, the toe control arm 27 has astrength lower than the other components of the suspension arm 11 so asto weaken the suspension arm 11 in strength. With respect to theexcessive force F to the components of the suspension arm 11 from thewheel 45, the toe control arm 27 is deformed before the other componentsare, so that the other components, being the upper arm 24 and the firstand second lower arms 25, 26, are protected.

[0038] The above embodiment of the present invention is described withrespect to rear suspension. The description is not intended to belimiting. The prevent invention can be applied to front suspension inwhich a suspension arm has a strength lower than that of a subframe.

[0039] Obviously, various minor changes and modifications of the presentinvention are possible in the light of the above teaching. It istherefore to be understood that within the scope of the appended claims,the invention may be practiced otherwise than as specifically described.

[0040] The present disclosure relates to the subject matter of JapanesePatent Application No. 2000-334613, filed Nov. 1, 2000, the disclosureof which is incorporated herein by reference in its entirety.

What is claimed is:
 1. A suspension structure comprising: a subframedesigned to be mounted to a floor panel; and a suspension arm mounted tosaid subframe vertically movably, said subframe being die-cast from analuminum alloy material, said suspension arm having strength lower thanthat of said subframe.
 2. A suspension structure as set forth in claim1, wherein said suspension arm comprises a toe control arm and othercomponents, and said toe control arm has strength lower than those ofsaid other components so that said suspension arm has strength lowerthan that of said subframe.
 3. A suspension structure as set forth inclaim 2, wherein said toe control arm is of a forged material.